Disc brakes are commonly used for braking heavy vehicles such as trucks, buses and coaches.
Disc brakes conventionally comprise a brake carrier and a caliper. The brake carrier is arranged to carry brake pads on each side of a rotor. The caliper is slidably mounted on the brake carrier by two or more guide assemblies, such that when the disc brake is actuated, the caliper is able to slide with respect to the brake carrier so as urge the brake pads onto a rotor in a clamping action and thereby effect braking.
A guide assembly typically comprises a guide pin along which the caliper can slide and a bore disposed in the caliper for receiving the guide pin.
To achieve free sliding of the caliper in a broad range of operating conditions, the guide assemblies must take account of manufacturing tolerances, effects of heating or cooling in use, and accommodate deflections of the disc brake due to the braking torque.
Previously, it has been found that these constraints can be compensated by inserting an oval, solid guide bush in the bore to guide the guide pin, the diameter of the oval being approximately 2 mm greater in the lateral direction where play is required than in the other, perpendicular direction. However, this solution is undesirable because the manufacture and insertion of oval, solid guide bushes (for example, by using a casting or sintering process) is complex, time consuming and expensive.